Final rinse step in phosphating of metals

ABSTRACT

Finally rinsing a phosphated metal surface with a molybdenum type rinse, such as a dilute aqueous solution of molybdenum oxide and an inorganic acid, preferably nitric acid, and which may also include ammonia.

United States Patent [191 Charles et al.

[ 5] June 25, 1974 FINAL RINSE STEP IN PHOSPHATING OF METALS [75] Inventors: Harry R. Charles, Troy; Donald L.

Miles, Bloomfield Hills, both of Mich.

[73] Assignee: Chemfil Miles Chemical & Filter Co., Inc., Troy, Mich.

22 Filed: June 15, 1972 21 Appl. No.: 263,004

UNITED STATES PATENTS 2,839,439 6/1958 Stapleton 148/6.l5 R

3,097,978 7/1963 Newell 148/6.14 R 3,136,663 6/1964 McDonald 148/615 R 3,695,942 10/1972 Binns 148/6.l5 R

Primary ExaminerRalph S. Kendall Attorney, Agent, or FirmCullen, Settle, Sloman & a qtww 5 7] ABSTRACT Finally rinsing a phosphated metal surface with a molybdenum type rinse, such as a dilute aqueous solution of molybdenum oxide and an inorganic acid, preferably nitric acid, and which may also include ammonia.

6 Claims, No Drawings FINAL RINSE STEP IN PHOSPHATING OF METALS FIELD OF THE INVENTION Phosphating of metal surfaces is well known, and often includes a final rinse step.

Chromium type rinses have been widely used but have come under attack because chromium is toxic and is considered to be a hazard to the environment.

The disclosed final rinse, not including chromium, is an important contribution to the known phosphating methods. The preferred final rinse solution is capable of performing the functions of the chromium rinses and is preferably non-toxic.

SUMMARY OF THE INVENTION The disclosed final rinse step is particularly suitable in the well known phosphating of ferrous metal surfaces. The exact details of the phosphating method are not critical to the disclosed final rinse step.

In the final rinsing step, the phosphated metal surface is rinsed with a weak aqueous solution of molybdenum oxide and an inorganic acid, preferably nitric acid. The preferred composition of the rinse solution may also include ammonia, such that the ammonia composition of the bath or rinse solution is approximately 2 to l, by weight, to the concentration of molybdenum oxide and the molybdenum nitrate composition is about 100 to 150 parts per million.

DESCRIPTION OF THE PREFERRED METHOD AND EXAMPLES As stated hereinabove, the specific phosphating method to which the final rinse is applied, is not critical to the present invention. It is of course understood that the term phosphating means the treatment of ferrous as well as zinci ferrous work pieces in phosphoric acid solutions.

One exemplary phosphating method uses a diluted concentrate including phosphoric acid, nitric acid, and zinc oxide or other suitable metal oxides including iron and manganese. Zinc may be utilized in the phosphating. Finally, the phosphated surface is rinsed.

The preferred composition of the final rinse solution may be formed by dissolving the molybdenum as an oxide in nitric acid, forming molybdic nitrate. Aqueous ammonia may be added to neutralize some of the free acid, which also forms a complex of ammonia molybdenum nitrate. This rinse concentrate is then diluted with water to a suitable concentration and the freshly phosphated work piece is either sprayed with a rinse solution or dipped in a rinse solution bath. The preferred composition thus includes molybdic oxide, nitric acid, ammonia and water.

Several examples of a suitable rinse solution could be given here, however it is believed to be within the skill of the art to vary the following concentrations to achieve various specific results and for particular applications.

A suitable rinse bath concentration was formed utilizing ten pounds of molybdenum oxide, twenty seven pounds of aqueous ammonia, 16 gallons of water and 133 pounds of nitric acid, resulting in approximately 10 gallons of concentrate. The concentrate was then further diluted with water, at the site, to provide approximately to parts per million of molybdenum nitrate. The freshly treated surface was rinsed with this solution for approximately 30 seconds, with very satisfactory results. A similar rinse composition was made without the aqueous ammonia and, although the result was not as good as the above example, it was found satisfactory.

As stated hereinabove, molybdenum is not considered toxic and the utiliziation of molybdenum in the final rinse solution, rather than chromium, greatly reduces the problems of disposing of the waste solution and reduces the damage to the environment caused by present phosphating methods.

The phosphating with which we are concerned is that type of phosphating known as pre-paint phosphating, as contrasted from phosphating used for oil retention, corrosion resistance, or phosphating for wear resistance. In the former case, the phosphating prepares the surface for painting; and is fundamentally a treatment with a metallic oxide, of the zinc or iron, etc., type all well known, and a phosphoric acid of the nitrate-nitrite type, also well known. This type of phosphating, very well known, prepares the surface for painting. It is in this type of phosphating that the disclosed final rinse step is employed instead of the chromium type final rinse step presently employed.

We claim:

1. In a pre-paint phosphating method, wherein a ferrous metal surface or a zinci ferrous surface is first treated with a zinc di-hydrogen phosphate solution or a solution of mono sodium or mono ammonium phosphate salts;

a separate and subsequent rinse step which comprises immersing the phosphated metal surface in an aqueous solution consisting essentially of molybdenum oxide, an inorganic acid, ammonia and water.

2. The method defined in claim 1, wherein the molybdenum nitrate concentration in the rinse is 100 to 150 parts per million.

3. The method defined in claim 2, wherein the concentration of ammonia in the rinse is about 2 to l, by weight, of ammonia to molybdenum oxide.

4. The method defined in claim 2, wherein the inorganic acid is a weak solution of nitric acid.

5. A method of treating a ferrous metal, prior to painting and following phosphating of the metal surface by conventional methods, comprising;

rinsing the phosphated metal surface in a separate step, remote from the phosphating treatment, with a weak aqueous solution of a nitric acid and 100 to 150 parts per million of molybdenum nitrate.

6. The method defined in claim 5, wherein the rinse includes about 2 to 1 percent, by weight, ammonia to molybdenum oxide. 

2. The method defined in claim 1, wherein the molybdenum nitrate concentration in the rinse is 100 to 150 parts per million.
 3. The method defined in claim 2, wherein the concentration of ammonia in the rinse is about 2 to 1, by weight, of ammonia to molybdenum oxide.
 4. The method defined in claim 2, wherein the inorganic acid is a weak solution of nitric acid.
 5. A method of treating a ferrous metal, prior to painting and following phosphating of the metal surface by conventional methods, comprising; rinsing the phosphated metal surface in a separate step, remote from the phosphating treatment, with a weak aqueous solution of a nitric acid and 100 to 150 parts per million of molybdenum nitrate.
 6. The method defined in claim 5, wherein the rinse includes about 2 to 1 percent, by weight, ammonia to molybdenum oxide. 